The present invention relates to a radial roller bearing and, in particular, to a radial roller bearing of a type that, in the end portion of a ring, there is formed a flange portion to be slidingly contactable with the end face of a cylindrical roller.
In a radial roller bearing using a cylindrical roller as a rolling element, in the end portion of a ring, there is formed a flange portion; that is, the end face of the cylindrical roller is slidingly contacted with the present flange portion to thereby control the attitude of the cylindrical roller when it is skewed, or guide the cylindrical roller in the circumferential direction of the ring, or support an axial load applied to the cylindrical roller.
In the radial roller bearing of this type, in case where only the radial load acts on the cylindrical roller and no skew moment occurs in the cylindrical roller, there is raised no problem even when the end face of the cylindrical roller is formed in a straight shape. However, in case where an axial load acts on the cylindrical roller and skew moment or a tilt angle occurs in the cylindrical roller, since the axial load is supported by the contact portion between the cylindrical roller and flange portion, an edge load is generated in the end portion of the contact portion. Due to this edge load, there is applied excessively large surface pressure onto the end portion of the contact portion, with the result that seizure and wear are easy to occur in the end portion of the contact portion. On this account, in a case of that a roller bearing is used under a condition that a certain level of axial load is applied thereon, a tapered roller bearing is chosen in many case. However, the tapered roller bearing needs to adjust the axial clearance between the cup and the cone, which determines the radial clearance and the bearing performances. So, when assembling the bearing into a housing, there is a need to locate the axial position of the cup and the cone precisely. On the other hand, when using cylindrical roller bearing, there is no need to locate the axial position precisely. So, it is very easy to assemble the bearing. The reason why, in case of that the cylindrical roller bearing is used instead of the tapered bearing, it is improved a convenience of assembling. If the axial load capacity of the cylindrical roller bearing is improved, the cylindrical roller bearing ban be used, instead of the tapered roller bearing, under a certain level of axial load. Thus in order to reduce the edge load applied to the cylindrical roller bearing under a certain level of axial load is applied thereon, as shown in FIG. 9, there is known a radial roller bearing in which the end face 13a of a cylindrical roller 13 to be contacted with a flange portion 14 is formed in a spherical shape having a given radius of curvature η.
However, in the radial roller bearing in which the end face of a cylindrical roller is formed in a spherical shape, since the center of the radius of curvature η lies on its rotation axis 13b of the cylindrical roller 13, as shown in FIG. 10, the contact portion 15 of the cylindrical roller with the flange portion 14 provides almost a circular shape. For this reason, in case where the radius of curvature η increases as the opening angle δ of the flange portion 14 decreases, the diameter of the contact portion 15 also increases and thus the contact portion 15 swells out of the flange portion 14, so that an edge load is easy to occur.